July 2017

Ankle sprain and the brain: Experts explore role of CNS function

In the moment: Sports medicine

Research presented in late June at the National Athletic Trainers Association (NATA) annual meeting in Houston, TX, adds to the evidence suggesting alterations in central nervous system (CNS) function play a role in chronic ankle instability (CAI).

NATA presentations also suggest, however, that the CAI patient population may be as heterogeneous with regard to CNS involvement as it is with regard to other functional characteristics.

Most studies in this area have focused on the extent to which various measures of spinal and corticospinal excitability can differentiate CAI patients from ankle sprain copers and healthy controls. But new research from the University of Kentucky in Lexington goes a step further, suggesting coordination between corticospinal excitability and inhibition in patients with CAI also has kinematic effects that could affect the risk of subsequent injury.

The investigators found the ratio of motor evoked potential (indicating cortical excitability) to cortical silent period (indicating cortical inhibition) was significantly correlated with ankle dorsiflexion during landing in CAI patients, but not in copers. Less cortical excitability relative to inhibition was associated with less ankle dorsiflexion, which can lead to stiff landings and increased risk of injury.

“This may describe a mechanism contributing to initial or recurrent lateral ankle sprain in this population,” said Colin Drinkard, MS, ATC, LAT, a former graduate student at the university and now an athletic trainer with Spectrum Health in Grand Rapids, MI, who presented the findings at the NATA meeting.

Clinicians should incorporate interventions aimed at a variety of dynamic sports-related tasks to help reboot the corticospinal pathways in patients with CAI, Drinkard said.

Previous research has suggested motor control in patients with CAI is less automatic—more dependent on cortical activity than spinal—than in healthy individuals (see “CAI and the CNS: Excitability may enhance instability,” May 2016, page 13). At the NATA meeting, new findings from the University of Miami in Coral Gables, FL, suggests this phenomenon becomes apparent acutely after an initial ankle sprain, which implies patients who become chronically unstable are unable to correct that corticospinal shift.

In 19 individuals assessed within 72 hours of an ankle sprain, the ratio of maximum Hoffman reflex to motor wave amplitude was significantly lower—in both the injured and contralateral limbs—than in 19 controls with no history of sprain, suggesting reduced spinal excitability.

Research from the University of North Carolina at Charlotte, however, suggests associations between CAI severity and cortical activity during movement may vary within the CAI population.

Investigators analyzed electroencephalographic data for 10 patients with self-reported CAI as they performed a standing task that involved leaning in three directions. The self-reported number of episodes of giving way, which served as an indicator of CAI severity for each participant, was significantly correlated with motor-related cortical potentials while leaning toward the involved and uninvolved limbs.

However, this correlation was driven by just a few outliers, said Christopher Burcal, MSc, ATC, a doctoral student in the university’s Biodynamics Research Lab, who presented the findings at the NATA meeting.

“A big issue with chronic ankle instability is heterogeneity; there are inherent outliers within our population,” Burcal said. “Our findings suggest that we may be seeing this for cortical activity as well as other measures.”

Neurocognitive factors

Given the increasing number of studies suggesting an association between corticospinal excitability and CAI, some researchers are exploring the possibility of an association between CAI and neurocognitive function—for which a number of clinically useful screening tools have been developed, thanks in part to recent interest in concussion. Although researchers have not yet identified a direct association between corticospinal excitability and neurocognitive measures in patients with CAI, a 2015 study reported significant correlations between corticospinal inhibition and neurocognitive outcomes in acutely concussed Australian amateur football players.

In a study of 15 patients with CAI presented at the NATA meeting, researchers found perceived disability was significantly associated with neurocognitive function, assessed using the CNS Vital Signs (CNSVS) tool. Better perceived ankle function was significantly associated with better overall CNSVS scores as well as scores for visual memory and reaction time.

“We may be missing something in terms of our CAI rehabilitation,” said Adam Rosen, PhD, ATC, an assistant professor in the School of Health and Kinesiology at the University of Nebraska Omaha, who presented the findings in Houston. “Maybe focusing more on neurocognitive factors during rehab may help improve function in these patients.”

But the theme of heterogeneity in the CAI population appears to extend to neurocognitive measures as well as cortical activity, according to findings from Ohio University in Athens that were presented at the NATA meeting.

In 16 participants who had self-reported CAI, the researchers found neurocognitive performance on a battery of Bertec vision training tests did not differ significantly from 34 healthy controls. However, the mean score for the CAI patients on the Activities of Daily Living subset of the Foot and Ankle Ability Measure was 97.7%—indicating a very high level of function despite the self-reported instability, which may have affected the study results.

“It’s possible that our findings are related to the fact that there are different levels of CAI severity,” said Nikki Jackson, MS, AT, a graduate assistant athletic trainer at the university, who presented the findings in Houston.